1. Field of the Invention
The present invention relates to a pneumatic tire which has improved early wear performance in a shoulder portion, without deteriorating noise performance.
2. Description of the Background Art
In a pneumatic tire, in particular, a pneumatic tire for passenger cars, flattening of tire of 70% or less tends to proceed, for example, as vehicles have higher outputs and higher speeds in recent years. As shown in FIG. 8, conventionally, tread contour shape x1 of such a flattened tire, that is, the contour line x1 of an outer surface of a tread portion on a tire meridian cross section, is formed by connecting a plurality of arcs whose radii of curvature r differ such that the radius of curvature becomes smaller sequentially toward the axial outer side of the tire (See Japanese Patent Application Publication No. 10-181309, and Japanese Patent Application Publication No. 10-287106).
However, in a tire with such a tread contour shape x1, a tire radius Tr on the side of a tread ground-contact edge Te significantly decreases, thus increasing amount of slippage with a road surface. Hence, there is a problem that wear speed of the shoulder portion sh is relatively fast, and lateral grooves to be arranged on the shoulder portion are worn out early.
The possibility of increasing groove depth of the lateral grooves is also considered to delay abrasion of the lateral grooves. However, increased groove depth might not only degrade noise performance, but also increase an amount of deformation due to reduced block rigidity of the shoulder portion, thus further deteriorating wear resistance.